U.S. patent number 7,866,434 [Application Number 12/186,858] was granted by the patent office on 2011-01-11 for steering apparatus.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Kohtaro Shiino, Akira Takahashi, Toshiro Yoda.
United States Patent |
7,866,434 |
Shiino , et al. |
January 11, 2011 |
Steering apparatus
Abstract
A steering apparatus includes an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed,
and a lower suspension-system control arm adapted to be
oscillatingly supported at one end on a vehicle body and having a
turning portion provided at the other end for pivotably supporting
the axle housing by the turning portion. An electric motor is
installed on the lower arm for turning the axle housing by a
driving force produced by the motor. A rotation axis of the motor
and a pivot of the axle housing are arranged to be offset from each
other.
Inventors: |
Shiino; Kohtaro (Isehara,
JP), Takahashi; Akira (Isehara, JP), Yoda;
Toshiro (Higashimatsuyama, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
40299318 |
Appl.
No.: |
12/186,858 |
Filed: |
August 6, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090057050 A1 |
Mar 5, 2009 |
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Foreign Application Priority Data
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Aug 28, 2007 [JP] |
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2007-220691 |
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Current U.S.
Class: |
180/411; 180/412;
280/93.512 |
Current CPC
Class: |
B62D
5/0418 (20130101); B62D 7/08 (20130101); B60G
7/006 (20130101); B62D 7/18 (20130101); B60G
2206/1116 (20130101); B60G 2204/419 (20130101) |
Current International
Class: |
B62D
5/04 (20060101); B62D 7/18 (20060101) |
Field of
Search: |
;180/411,412
;280/93.512 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2007-1564 |
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Jan 2007 |
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JP |
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2007-55409 |
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Mar 2007 |
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JP |
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Primary Examiner: Morris; Lesley
Assistant Examiner: Arce; Marlon A
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
What is claimed is:
1. A steering apparatus, comprising: an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed;
a lower arm adapted to be oscillatingly supported at one end on a
vehicle body and having a turning portion provided at the other end
for pivotably supporting the axle housing by the turning portion;
an electric motor installed on the lower arm for turning the axle
housing by a driving force produced by the motor; and a speed
reducer configured to reduce rotation of the motor and installed on
the lower arm and located between a rotation axis of the motor and
the turning portion; wherein the rotation axis of the motor and a
pivot of the axle housing are arranged to be offset from each
other, and wherein the rotation axis of the motor is laterally
spaced apart from the turning portion and arranged closer to the
vehicle body rather than the turning portion.
2. The steering apparatus as claimed in claim 1, wherein: the
turning portion is mechanically linked via a universal joint to the
axle housing.
3. The steering apparatus as claimed in claim 1, wherein: the
rotation axis of the motor is arranged along a pivot that
oscillatingly supports the lower arm; and the speed reducer
comprises a worm gear and a worm wheel.
4. The steering apparatus as claimed in claim 3, wherein: the motor
is installed on an upside of the lower arm.
5. The steering apparatus as claimed in claim 4, wherein: the lower
arm is pivotally supported on the vehicle body between two
lower-arm supporting portions attached to the vehicle body and
spaced apart from each other; and the motor is located between the
two lower-arm supporting portions.
6. The steering apparatus as claimed in claim 4, further
comprising: a tie rod displaceable in a vehicle lateral direction
responsively to rotary motion of the motor; and a knuckle arm
integrally connected to the axle housing and mechanically linked to
the tie rod, wherein a straight line, passing through a rotation
center of a turning pair of the tie rod and the knuckle arm and a
rotation center of a turning pair of the lower arm and the axle
housing, is arranged substantially parallel to the pivot of the
lower arm.
7. The steering apparatus as claimed in claim 3, wherein: the speed
reducer is accommodated in a speed-reducer casing and has a sector
gear; and the speed-reducer casing has a stopper mechanism formed
in the casing for restricting anticlockwise and clockwise angular
displacements of the sector gear exceeding predetermined
angular-displacement limits by way of abutment with the sector
gear.
8. The steering apparatus as claimed in claim 1, wherein: the motor
and the speed reducer are provided for each individual steered road
wheel.
9. A steering apparatus, comprising: an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed;
a lower arm adapted to be oscillatingly supported at one end on a
vehicle body and having a turning portion provided at the other end
for pivotably supporting the axle housing by the turning portion;
an electric motor installed on the lower arm for turning the axle
housing by a driving force produced by the motor; and a
harmonic-drive speed reducer configured to reduce rotation of the
motor, wherein a rotation axis of the motor and a pivot of the axle
housing are arranged to be offset from each other, and wherein the
rotation axis of the motor is laterally spaced apart from the
turning portion and arranged closer to the vehicle body rather than
the turning portion.
10. A steering apparatus, comprising: an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed;
a lower arm adapted to be oscillatingly supported at one end on a
vehicle body and having a turning portion provided at the other end
for pivotably supporting the axle housing by the turning portion;
an electric motor installed on the lower arm for turning the axle
housing by a driving force produced by the motor; and a speed
reducer configured to reduce rotation of the motor and installed on
the lower arm and located between the motor and the turning
portion, wherein the motor is arranged closer to the vehicle body
rather than a steering axis serving as a pivot of the axle.
11. The steering apparatus as claimed in claim 10, wherein: the
motor is installed on an upside of the lower arm.
12. The steering apparatus as claimed in claim 11, further
comprising: a steering controller configured to control the motor,
the steering controller installed on the lower arm.
13. The steering apparatus as claimed in claim 10, wherein: the
motor and the speed reducer are provided for each individual
steered road wheel.
14. A steering apparatus, comprising: an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed;
a lower arm adapted to be oscillatingly supported at one end on a
vehicle body and having a turning portion provided at the other end
for pivotably supporting the axle housing by the turning portion;
an electric motor installed on the lower arm for turning the axle
housing by a driving force produced by the motor; and a
harmonic-drive speed reducer configured to reduce rotation of the
motor, wherein the motor is arranged closer to the vehicle body
rather than a steering axis serving as a pivot of the axle
housing.
15. A steering apparatus, comprising: an axle housing rotatably
supporting a wheel hub on which a steered road wheel is installed;
a lower arm adapted to be oscillatingly supported at one end on a
vehicle body and pivotably supporting the axle housing at the other
end; an electric motor installed on the lower arm for turning the
axle housing by a driving force produced by the motor; and a speed
reducer configured to reduce rotation of the motor, wherein the
motor and the speed reducer are arranged from the vehicle body in
that order.
16. The steering apparatus as claimed in claim 15, wherein: the
motor is installed on an upside of the lower arm.
Description
TECHNICAL FIELD
The present invention relates to a steering apparatus, and
specifically to an automotive steer-by-wire (SBW) vehicle steering
system configured to steer a plurality of steered road wheels
independently of each other by means of respective steering
actuators.
BACKGROUND ART
In recent years, there have been proposed and developed various
automotive steer-by-wire (SBW) vehicle steering systems in which a
steering reaction torque applied to a steering wheel and a steer
angle at each steered road wheel can be arbitrarily determined.
Such an automotive SBW vehicle steering apparatus generally employs
a pair of steering actuators, each mechanically disconnected from a
steering wheel. One such SBW vehicle steering apparatus, which is
configured to steer a plurality of steered road wheels
independently of each other by means of respective steering
actuators, has been disclosed in Japanese Patent Provisional
Publication No. 2007-55409 (hereinafter is referred to as
"JP2007-055409"), corresponding to United States Patent Application
Publication No. US 2007/0045036 A1 and also disclosed in Japanese
Patent Provisional Publication No. 2007-1564 (hereinafter is
referred to as "JP2007-001564"). In a steering device (or a turning
device including a turning motor and a speed reducer) disclosed in
JP2007-055409, in order to avoid undesired interference between a
steering actuator (or a turning actuator) and a hub carrier (a
road-wheel side component part provided between upper and lower
control arms), the turning actuator is laid out, such that the
rotation axis of the turning actuator and the kingpin axis (serving
as a turning center of the steered road wheel) are arranged
substantially coaxial with each other. On the other hand, in a
steer-by-wire system disclosed in JP2007-001564, in order to
enhance the layout flexibility of engine component parts by
compactifying the SBW system, a steering actuator is fixed onto or
mounted on the vehicle body. The output (i.e., rotary motion) of
the steering actuator is converted into oscillating motion of a
pitman arm. The oscillating motion of the pitman arm is further
transmitted through a linkage, such as a tie rod and a steering
knuckle arm, so as to steer or turn the associated steered road
wheel.
SUMMARY OF THE INVENTION
Generally, to convert rotary motion of an electric motor into
torque needed to turn the steered road wheel, a speed reducer
having a high reduction ratio must be combined with the electric
motor. Conversely speaking, to downsize a speed reducer, a
high-torque motor must be used. For instance, a speed reducer can
be eliminated by using a direct-drive motor. However, in such a
case, the direct-drive motor itself must be large-sized to produce
a required torque. Therefore, the overall size and gross weight of
the steering actuator, which is constructed by the electric motor
and the speed reducer, are determined depending on a required
torque (i.e., a design maximum torque output).
In the steering device (the turning device) disclosed in
JP2007-055409, the steering actuator is installed on the outside
end of the lower arm of the suspension system. The outside end of
the lower arm serves as a lower pivot of the kingpin axis (that is,
the steering axis). As previously discussed, the steering actuator,
constructed by a speed-reducer-equipped motor or a direct-drive
motor, requires a specified size and weight, determined based on a
required torque. Therefore, practically, it is very difficult to
install the steering actuator, having the specified size and weight
based on the required torque, on the outside end of the
suspension-system control arm coaxially with the kingpin axis,
while avoiding undesired interference with road-wheel side
component parts, for example, a hub carrier or a tire. In other
words, it is very difficult to install the steering actuator on the
outside end of the suspension-system control arm, while ensuring an
adequately high reduction ratio (that is, an adequately high torque
produced to turn the steered road wheel).
As discussed previously, the steering actuator, constructed by a
speed-reducer-equipped motor, requires a specified size and weight,
determined based on a required torque. Additionally, the steering
actuator having the specified weight is installed on the outside
end of the suspension-system lower arm (i.e., the road-wheel side
installation position of the lower arm). This means an increase in
a moment of load acting on the lower arm, in other words, an
increase in unsprung mass (unsprung weight), thereby deteriorating
driving stability (both vehicle driveability and vehicle stability)
and riding comfort.
On the other hand, in the SBW system of JP2007-001564, the steering
actuator is installed on the vehicle body, and additionally the
steering actuator, constructed by a speed-reducer-equipped motor,
requires a specified size and weight, determined based on a
required torque. Thus, there is a possibility of undesired
interference between the steering actuator and vehicle-body side
component parts (such as engine component parts). Therefore, there
is a limit for layout flexibility improvement. In addition to the
above, the tie rod is mechanically linked to the steering actuator
installed on the vehicle body, and thus, during suspension stroke,
toe changes occur owing to the positional relationship (the
suspension geometry) between the tie rod and the suspension-system
control arm. Such toe changes can be compensated for by controlling
the respective steering actuators, but the toe-change compensation
requires a new control logic (i.e., additional arithmetic and
logical operations), thereby resulting in the undesirably
complicated SBW system.
It is, therefore, in view of the previously-described disadvantages
of the prior art, an object of the invention to provide a steering
apparatus configured to enhance its layout flexibility and
saleability, without sacrificing riding comfort.
In order to accomplish the aforementioned and other objects of the
present invention, a steering apparatus comprises an axle housing
rotatably supporting a wheel hub on which a steered road wheel is
installed, a lower arm adapted to be oscillatingly supported at one
end on a vehicle body and having a turning portion provided at the
other end for pivotably supporting the axle housing by the turning
portion, and an electric motor installed on the lower arm for
turning the axle housing by a driving force produced by the motor,
wherein a rotation axis of the motor and a pivot of the axle
housing are arranged to be offset from each other.
According to another aspect of the invention, a steering apparatus
comprises an axle housing rotatably supporting a wheel hub on which
a steered road wheel is installed, a lower arm adapted to be
oscillatingly supported at one end on a vehicle body and having a
turning portion provided at the other end for pivotably supporting
the axle housing by the turning portion, and an electric motor
installed on the lower arm for turning the axle housing by a
driving force produced by the motor, wherein the motor is arranged
closer to the vehicle body rather than a steering axis serving as a
pivot of the axle housing.
According to a further aspect of the invention, a steering
apparatus comprises an axle housing rotatably supporting a wheel
hub on which a steered road wheel is installed, a lower arm adapted
to be oscillatingly supported at one end on a vehicle body and
pivotably supporting the axle housing at the other end, an electric
motor installed on the lower arm for turning the axle housing by a
driving force produced by the motor, and a speed reducer configured
to reduce rotation of the motor, wherein the motor and the speed
reducer are arranged from the vehicle body in that order.
The other objects and features of this invention will become
understood from the following description with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view illustrating a first
embodiment of an automotive vehicle steering apparatus (only the
front-left side), as viewed from the front face of the vehicle.
FIG. 2 is a partial cross-sectional view illustrating a second
embodiment of an automotive vehicle steering apparatus (only the
front-left side), taken along the line C-C in FIG. 3, as viewed
from the front face of the vehicle.
FIG. 3 is a partial cross-sectional view illustrating the steering
apparatus (only the front-left side) of the second embodiment, as
viewed from the upside of the vehicle.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
Referring now to the drawings, particularly to FIG. 1, the steering
apparatus 1 of the first embodiment is exemplified in a so-called
steer-by-wire (SBW) system of an automotive vehicle, in which
front-left and front-right steered road wheels FL, FR, each
rotatably supported by a suspension system 2, are steered
independently of each other by driving forces produced by
respective steering actuators, each comprised of an electric motor
and a speed reducer.
The SBW system includes a steering input device (i.e., a steering
wheel or the like), steered road wheels (front-left and front-right
steered road wheels FL-FR), which are mechanically disconnected
from the steering input device, a steering angle sensor (e.g., a
steering wheel angle sensor) provided to electrically detect an
angular displacement (e.g., a steering wheel angle) of the steering
input device measured from the straight ahead position
(corresponding to zero average steer angle of the front-left and
front-right steered road wheels), a steering torque sensor provided
to electrically detect the magnitude and direction of steering
torque applied to the steering input device, a pair of steering
actuators that produce driving torques (or driving forces) by which
respective steered road wheels FL-FR are steered independently of
each other, and a steering electronic control unit (a steering
controller) S-ECU configured to calculate at least a steer angle of
each of the steered road wheels FL-FR, based on a sensor signal
from the steering angle sensor, for controlling the operation (the
magnitude and sense of driving torque) of each of the steering
actuators. In a similar manner to a conventional SBW system, the
steering input device is mechanically connected to a steering
reaction-torque actuator (simply, a reaction actuator) that applies
a reaction torque (or a feedback torque) to the steering input
device (e.g., the steering wheel).
The steering controller S-ECU is electrically connected to both the
steering actuator (comprised of an electric motor 50 and a speed
reducer 60 both described later) and the reaction actuator. The
S-ECU is also connected electrically to a vehicle electronic
control unit (a vehicle controller) V-ECU. The V-ECU generally
comprises a microcomputer. The V-ECU includes an input/output
interface (I/O), memories (RAM, ROM), and a microprocessor or a
central processing unit (CPU). The input/output interface (I/O) of
the V-ECU receives input information from various engine/vehicle
sensors, for example, a suspension stroke sensor installed on
suspension system 2, wheel speed sensors, each installed on a wheel
hub H (a center part of the road wheel), and the like. Within the
V-ECU, the central processing unit (CPU) allows the access by the
I/O interface of input informational data signals from the
previously-discussed engine/vehicle sensors. The CPU of the V-ECU
is responsible for carrying the control program stored in memories
and is capable of performing necessary arithmetic and logic
operations containing vehicle speed control, wheel speed control,
yaw rate control, and the like. Computational results, that is,
calculated output signals are relayed through the output interface
circuitry of the V-ECU to output stages (e.g., a throttle actuator,
an automatic brake actuator or a hydraulic brake modulator, and the
like). The V-ECU is also configured to send out vehicle information
(e.g., vehicle speed) and a desired steer angle at each steered
road wheel to the S-ECU.
As discussed above, the steering controller S-ECU receives sensor
signals from the engine/vehicle sensors via the V-ECU and sensor
signals from the steering angle sensor and the steering torque
sensor, and then calculates, based on the input information, a
driving torque (exactly, the magnitude and sense of driving torque
to be produced by each steering actuator (especially, motor 50).
Thereafter, the S-ECU generates control command signals
corresponding to the calculated driving torques to the respective
steering actuators during the steer-by-wire (SBW) operating mode.
Additionally, the S-ECU calculates a reaction force acting on the
tire (the steered road wheel) by the road surface, based on the
previously-noted vehicle information and the electric current
applied to each of the steering actuators and the rotation angle of
each of the steering actuators. The S-ECU also generates a control
command signal corresponding to the calculated road-surface
reaction force to the reaction actuator during the SBW operating
mode. In the SBW system as discussed above, there are the following
several merits.
The adoption of such an SBW system ensures the enhanced layout
flexibility and the increased degree of freedom of design for
steering-system component parts. Therefore, it is possible to
realize the compact steering system. Additionally, in the SBW
system in which front-left and front-right steered road wheels
FL-FR can be steered independently of each other by means of
respective steering actuators, it is possible to properly maximize
cornering forces produced by respective front-left and front-right
steered road wheels FL-FR by actively changing a ratio between
steer angles at the front-left and front-right steered road wheels,
thereby enhancing the maneuverability of the vehicle. Furthermore,
on front-wheel-drive vehicles, by way of active toe-change, it is
possible to actively compensate for toe-in, occurring due to a
driving force resulting from driving torque application to each of
front steered road wheels FL-FR and a suspension elasticity of each
of front suspension systems 2, 2, thereby effectively reducing a
rolling resistance force resulting from energy losses due to
deformations of each of front steered road wheels FL-FR. This
contributes to the reduced fuel consumption rate.
(Steering System Configuration)
Steering apparatus 1 of the first embodiment, constructing a part
of the SBW system, which system is applied to a front-wheel-drive
vehicle, is hereunder described in detail in reference to FIG. 1.
Note that FIG. 1 shows the partial cross-sectional view of only the
front-left side of steering apparatus 1 of the first embodiment,
when viewed from the front face of the vehicle.
Suspension system 2 is a so-called strut type suspension system.
Suspension system 2 is comprised of a strut 10 employing both a
coil spring and a shock absorber for absorbing impact loads acting
in the vertical direction (in the direction of the vehicle z-axis),
a lower control arm (simply, a lower arm) 20 pivoted to a vehicle
body for pivotably supporting front-left steered road wheel FL to
the vehicle body, and an axle housing 30 rotatably supporting an
axle shaft AS.
Axle shaft AS is connected via a constant-velocity joint J (covered
by a protective boot) to the outside end of a drive shaft DS. Wheel
hub H is fixedly connected to the circumference of axle shaft AS,
for co-rotation with axle shaft AS. A wheel bearing 31 is
interposed between hub H and axle housing 30, for rotatably
supporting hub H on axle housing 30 via wheel bearing 31.
Front-left steered road wheel FL is installed onto hub H (exactly,
hub bolts of hub H) at the outside of wheel bearing 31 in the
lateral direction (in the direction of the vehicle y-axis). Axle
housing 30 has a first arm 32 extending upwards from the outer
periphery of the cylindrical-hollow portion of axle housing 30 and
a second arm 33 extending downwards from the cylindrical-hollow
portion of axle housing 30.
The lower end of strut 10 is mechanically linked to the first arm
32, whereas the upper end of strut 10 is connected via a strut
insulator to the vehicle body. Strut 10 is supported to rotate
about its strut axis, responsively to a pivoting motion of first
arm 32 (axle housing 30), occurring when the steered road wheels
are turned.
Lower arm 20 is an A-shaped lower control arm or a .GAMMA.-shaped
lower control arm, which is generally used as a strut-type front
suspension system. Lower arm 20 is pivotally or oscillatingly
supported on the vehicle body by means of two lower-arm pivots
(hereinafter are referred to as "supporting portions 21, 21")
spaced apart from each other in the vehicle longitudinal direction.
Each of supporting portions 21, 21 has the same structure as a
typical vehicle-body side control-arm supporting portion generally
applied to a typical A-shaped lower control arm (or a typical
.GAMMA.-shaped lower control arm) not employing a steering
actuator. Also, each supporting portion 21 is installed on the
vehicle body at the same installation position as the typical
vehicle-body side control-arm supporting portion. In the first
embodiment, supporting portion 21 is constructed by a cylindrical,
elastic or elastomeric bushing, which is comprised of an outer
bushing sleeve 210, an inner bushing shaft (or an inner bushing
sleeve) 211, and a rubber bushing 212 press-fitted between outer
and inner bushing sleeves 210 and 211. Each supporting portion 21
is installed on the vehicle body, such that the axis of supporting
portion 21 (the axis of the bushing) extends in the longitudinal
direction (in the direction of the vehicle x-axis).
Outer bushing sleeve 210 is formed integral with lower arm 20
(exactly, an arm portion 22 described later). As can be seen from
the lateral cross section of the rubber-bushed supporting portion
21 in FIG. 1, inner bushing sleeve 211 is provided inside of outer
bushing sleeve 210, interposing rubber bushing 212 between outer
and inner bushing sleeves 210-211. Inner bushing sleeve 211 is
fixed to or attached to the vehicle body. The axes of two
rubber-bushed supporting portions 21, 21 are arranged substantially
coaxial with each other in their longitudinal directions (in the
direction of the vehicle x-axis), and thus, in FIG. 1, only the
rubber-bushed supporting portion 21 of the near side is shown. That
is, the straight line, linking the axes of two rubber-bushed
supporting portions 21, 21, is arranged substantially in parallel
with the ground surface. Lower arm 20 is pivotally supported on the
vehicle body by means of two rubber-bushed supporting portions 21,
21 in such a manner as to oscillate about the previously-noted
straight line, linking the axes of supporting portions 21, 21,
substantially in the vertical direction of the vehicle (in the
direction of the vehicle z-axis). That is, the straight line
through the axes of supporting portions 21, 21 serves as the pivot
of oscillating motion of lower arm 20.
Lower arm 20 has the arm portion 22 extending laterally outwards
from the rubber-bushed supporting portions 21, 21 attached to the
vehicle body, and a turning portion 23 installed on the outside end
of lower arm 20. Second arm 33 of axle housing 30 is linked via a
universal joint 40 to turning portion 23. In the first embodiment,
a Hooke's joint, which consists of two yokes attached to their
respective shafts and connected by means of a spider, is used as
universal joint 40.
A plurality of gears 61-63, constructing speed reducer 60, are
built in arm portion 22. A rotational shaft (i.e., a rotation axis)
631 of the third gear 63 is installed in turning portion 23. A
driving-side yoke 41, whose axis is arranged coaxial with the axis
of rotational shaft 631 of third gear 63, is formed integral with
the upper face of third gear 63.
On the other hand, a driven-side yoke 42 is formed integral with
the lower end of second arm 33 of axle housing 30. Driving-side
yoke 41 and driven-side yoke 42 are connected by a spider 43. When
driving-side yoke 41 rotates together with third gear 63, rotary
motion of driving-side yoke 41 is transmitted through spider 43 to
driven-side yoke 42. As a result of this, second arm 33 turns or
pivots. That is, lower arm 20 pivotably supports axle housing 30 by
means of turning portion 23. The center of universal joint 40
serves as a lower outer pivot of front-left steered road wheel FL.
On the other hand, the installation point of the upper end of strut
10 to the vehicle body serves as an upper outer pivot of front-left
steered road wheel FL. Therefore, the straight line, linking the
installation point of the upper end of strut 10 to the vehicle body
(i.e., the upper outer pivot) and the center of universal joint 40
(i.e., the lower outer pivot), corresponds to a kingpin axis (i.e.,
a steering axis or a steer rotation axis) of front-left steered
road wheel FL.
Suppose that front-left steered road wheel FL travels on uneven
road surfaces during vehicle driving. Oscillating motion of lower
arm 20 occurs, and therefore front-left steered road wheel FL moves
into jounce or rebound. That is, up-and-down motion of front-left
steered road wheel FL relative to the vehicle body occurs. At this
time, impact loads inputted from the uneven road surface to
front-left steered road wheel FL can be effectively absorbed by
means of strut 10. Due to the oscillating motion of lower arm 20,
the angle between axle housing 30 and lower arm 20 tends to
slightly change. The angle change can be absorbed by universal
joint 40.
(Steering Actuator)
The steering actuator of steering apparatus 1 of the first
embodiment is comprised of motor 50 and speed reducer 60. The
steering actuator is installed on the upper face of lower arm 20 or
installed inside of lower arm 20. Speed reducer 60 includes a
parallel gear train comprised of three gears 61-63 whose rotation
axes are parallel to each other. First gear 61, second gear 62, and
third gear 63 are three different spur gears, which construct a
two-stage gear mechanism. First and second gears 61-62 are circular
spur gears, whereas third gear 63 is a sector gear. In the shown
embodiment, spur gears are used as gears 61-63. In lieu thereof,
helical gears may be used as gears 61-63.
It should be noted here that the "face" of lower arm 20 means
either one of upper and lower faces of lower arm 20 as viewed in
the vehicle vertical direction (in the direction of the vehicle
z-axis). The "upper face" of lower arm 20 means the upside of lower
arm 20, as viewed from above. The "lower face" of lower arm 20
means the underside of lower arm 20, as viewed from below.
Lower arm 20 has a first case 201 constructing the lower face of
lower arm 20 and a second case 202 constructing the upper face of
lower arm 20. First case 201 and second case 202 cooperate with
each other to provide a speed-reducer casing for speed reducer 60.
The speed-reducing gear train of speed reducer 60 is operably
accommodated in an internal space R defined by the inner peripheral
walls of first and second cases 201-202.
Electric motor 50 is a direct-current (DC) brushless motor.
Although it is not clearly shown in the drawings, an electric
current sensor and a motor rotation sensor are attached to motor
50, for detecting the magnitude of electric current flow through
motor 50 and the rotation angle of an output shaft 51 of motor 50.
The electric current sensor and the motor rotation sensor of motor
50 are electrically connected to the input interface circuitry of
the steering controller S-ECU. The motor unit, constructing motor
50, is an electric motor unit, generally used in an existing
electric-motor-driven power steering system.
Motor 50 is installed and fitted onto the upper face of second case
202. As viewed from above (in the top view of the vehicle), motor
50 is laid out, such that motor 50 and drive shaft DS are not
overlapped with each other. Thus, even when lower arm 20 oscillates
during suspension stroke, there is no risk that motor 50 comes into
contact with drive shaft DS. Output shaft 51 of motor 50 is
protruded into the internal space R in a manner so as to be
perpendicular to a plane of lower arm 20, that is, a plane through
the center A of oscillating motion of lower arm 20 and the center B
of the outside end portion of lower arm 20 (substantially
corresponding to the center of rotational shaft 631 of third gear
63). First gear 61 is fixedly connected to the tip of output shaft
51, for co-rotation with the motor output shaft.
Second gear 62 is provided in the internal space R in a manner so
as to be laid to be laterally outwards offset from output shaft 51
of motor 50. Second gear 62 is rotatably supported by means of a
first bearing BRG1 installed in first case 201 and a second bearing
BRG2 installed in second case 202. The rotation axis of second gear
62 is laid to be parallel to the rotation axis of output shaft 51
of motor 50. A large-diameter gear 621 and a small-diameter gear
622 are formed integral with the rotational shaft of second gear 62
to provide a two-stage gear configuration. Large-diameter gear 621,
located below small-diameter gear 622, is in meshed-engagement with
first gear 61.
Third gear 63 is provided in the internal space R and arranged to
be laterally outwards offset from second gear 62. Third gear 63 is
rotatably supported by means of a third bearing BRG3 installed in
first case 201 and a fourth bearing BRG4 installed in second case
202. The rotation axis of third gear 63 is laid to be parallel to
the rotation axis of second gear 62. The toothed portion of third
gear 63 (the sector gear) is in meshed-engagement with
small-diameter gear 622 of second gear 62. As previously described,
driving-side yoke 41, whose axis is arranged coaxial with the axis
of rotational shaft 631 of third gear 63, is formed integral with
the upper face of third gear 63. Driving-side yoke 41 is laid to
protrude from the upper face of lower arm 20 through a through hole
207 formed in second case 202.
The speed-reducer casing, constructed by first and second cases
201-202, is provided with a stopper mechanism (i.e., a pair of
stopper shoulders) that restricts excessive anticlockwise and
clockwise angular displacements of third gear 63 exceeding
predetermined angular-displacement limits by way of abutment of the
first stopper shoulder with one radially-extending sidewall portion
of third gear 63 (the sector gear) and abutment of the second
stopper shoulder with the other radially-extending sidewall portion
of third gear 63. The previously-discussed predetermined
angular-displacement limits are set or determined to be identical
to maximum leftward and rightward rotation angles of third gear 63
(the sector gear) under left-turn and right-turn limits. In the
first embodiment, third gear 63 is constructed by a sector gear,
and therefore it is possible to effectively reduce or shorten the
size and dimensions of lower arm 20 in the lateral and longitudinal
directions (in the directions of the y-axis and the x-axis of the
vehicle). Hence, it is possible to effectively suppress lower arm
20 from being lengthened than necessary, while adequately reducing
the motor speed, thereby enabling the compactified SBW system.
The number of revolutions of motor 50 (output shaft 51), simply,
the motor speed, is identical to the number of revolutions of first
gear 61. The motor speed (output rotation of motor 50) is reduced
by a ratio between the number of teeth on large-diameter gear 621
of second gear 62 and the number of teeth on first gear 61, and
then the reduced rotation is transmitted to second gear 62 as input
rotation. The output rotation of second gear 62 is reduced by a
ratio between the converted number of teeth on third gear 63 (based
on the assumption that third gear 63 is a circular gear whose
external teeth are circumferentially equidistant-spaced from each
other and integrally formed around its entire circumference) and
the number of teeth on small-diameter gear 622 of second gear 62.
The reduced output rotation of second gear 62 is transmitted to
third gear 63. Third gear 63 is configured to rotate within angular
displacements corresponding to steer angle limits. Thus, it is
unnecessary to rotate third gear 63 by an angular displacement of
360 degrees. For the reasons discussed above, the sector gear is
used as third gear 63.
In this manner, rotation of motor 50 is reduced by means of the
two-stage speed reducer 60 comprised of three gears 61-63, and thus
converted into rotary motion of driving-side yoke 41. As is
generally known, a speed reduction means a torque multiplication
(or a torque increase). Thus, an output torque generated from motor
50 is multiplied in proportion to the speed reduction ratio of the
two-stage speed reducer 60, and then the multiplied torque is
outputted to driving-side yoke 41. Rotation and torque of
driving-side yoke 41 are transferred via spider 43 to driven-side
yoke 42, to turn axle housing 30 (in other words, front-left
steered road wheel FL) about the kingpin axis (the steering axis).
The above-mentioned kingpin axis (the steering axis) serves as a
pivot of axle housing 30. That is, axle housing 30 (in other words,
front-left steered road wheel FL) is turned by a driving force of
motor 50 installed on lower arm 20.
As indicated by the phantom line in FIG. 1, the steering controller
S-ECU, which is configured to control motor 50, is installed or
mounted on lower arm 20 in close proximity to the motor.
In a similar manner to the front-left steering system configuration
as discussed previously, the steering actuator (motor 50 and speed
reducer 60) of steering apparatus 1 of the first embodiment is
installed on lower arm 20 of the front-right side. That is, the
steering actuator (50, 60) is installed on each individual steered
road wheel (FL, FR). These left and right steering actuators
construct a part of the SBW system.
Operation and Effects of First Embodiment
Steering apparatus 1 of the first embodiment provides the following
operation and effects.
(1) Steering apparatus 1 includes axle housing 30 rotatably
supporting hub H on which a steered road wheel (front-left or
front-right steered road wheel FL, FR) is installed, lower arm 20
adapted to be oscillatingly supported at one end (i.e., the inside
end of lower arm 20) on a vehicle body by means of supporting
portions 21, 21 corresponding to the inside lower-arm pivots
substantially coaxial with each other in the direction of the
vehicle x-axis, and having turning portion 23 provided at the other
end (i.e., the outside end of lower arm 20) for pivotably
supporting axle housing 30 by turning portion 23, and motor 50
installed on lower arm 20 for turning axle housing 30 by a driving
force produced by the motor. In the steering apparatus 1 of the
first embodiment, the rotation axis of motor 50 (i.e., the axis of
motor output shaft 51) and the pivot of axle housing 30 (i.e., the
kingpin axis or the steering axis) are arranged to be offset from
each other.
As set forth above, in steering apparatus 1 of the first
embodiment, constructing a part of the SBW system, motor 50 is
installed on lower arm 20, instead of installing the motor on the
vehicle body. Thus, there is no risk of undesired interference
between the steering actuator (e.g., motor 50) and vehicle-body
side component parts (such as engine component parts). Accordingly,
it is possible to enhance the system layout flexibility.
Additionally, in the case of the previously-noted steering output
section of steering apparatus 1 of the first embodiment, by virtue
of the layout of the steering actuator (especially, motor 50) on
lower arm 20, there is a less change in the positional relationship
between the steering actuator (i.e., motor 50) and the
suspension-system control arm (i.e., lower arm 20), and as a result
any toe change does not occur during suspension stroke. This
eliminates the necessity of a new control logic (i.e., additional
arithmetic and logical operations), required to compensate for toe
changes. Thus, it is possible to simplify the control system
configuration of the steering controller S-ECU, thus avoiding the
complicated SBW system.
Furthermore, the rotation axis of motor 50 and the pivot of axle
housing 30 (that is, the kingpin axis or the steering axis) are
arranged to be spaced apart from each other (in the vehicle lateral
direction), and thus it is possible to install speed reducer 60
between the rotation axis (motor output shaft 51) of motor 50 and
the kingpin axis. Therefore, it is possible to ensure adequate
steering torque, while avoiding undesired interference between the
steering actuator (e.g., motor 50) and road-wheel side component
parts (e.g., wheel hub H or a tire of a steered road wheel (e.g.,
front-left steered road wheel FL), thus enhancing the saleability.
Owing to the previously-noted offset layout of the rotation axis of
motor 50 and the kingpin axis, it is possible to reduce a moment of
the motor load acting on lower arm 20, thus effectively suppressing
an increase in unsprung mass of the vehicle. This effectively
avoids the driving stability and riding comfort from being
deteriorated, even under a condition where steering actuators are
installed on respective lower control arms.
(2) The rotation axis of motor 50 is laterally spaced apart from
turning portion 23 and arranged close to the vehicle body. In other
words, motor 50 is provided closer to the vehicle body rather than
the pivot of axle housing 30 (that is, the kingpin axis).
Therefore, it is possible to certainly prevent undesirable
interference between the steering actuator (e.g., motor 50) and
road-wheel side component parts (e.g., wheel hub H or a tire of a
steered road wheel (e.g., front-left steered road wheel FL). In
addition to the above, the distance between the installation
position of motor 50 and the axis of oscillating motion of lower
arm 20 (that is, the straight line through the axes of supporting
portions 21, 21) can be shortened. Owing to the shortened distance
between the installation position of motor 50 and the lower-arm
pivot (supporting portions 21, 21), it is possible to effectively
reduce a moment of the motor load acting on lower arm 20, thereby
certainly suppressing an increase in unsprung mass of the
vehicle.
(3) Moreover, in the lower-arm-mounted steering actuator
incorporated in steering apparatus 1 of the first embodiment, speed
reducer 60, which is configured to reduce rotation produced by
motor 50 and multiply torque generated from the motor, is provided.
Speed reducer 60 is installed on lower arm 20 and located between
the rotation axis of motor 50 and turning portion 23. In other
words, the steering actuator is arranged on the suspension-system
lower arm, such that motor 50 and speed reducer 60 are arranged
from the vehicle body side, in that order.
In comparison with a so-called coaxial layout in which the rotation
axis of an electric motor and an output shaft of a speed reducer
are arranged coaxial with each other, in the case of an offset
layout (or a parallel layout) of steering apparatus 1 of the first
embodiment in which the rotation axis of motor 50, the rotation
axis of second gear 62, and the rotation axis (rotation shaft 631)
of third gear 63 are parallel to and offset from each other, it is
possible to downsize the motor unit itself. In the case of the
parallel layout, the axial length of the motor unit can be reduced,
as compared to the coaxial layout. Especially, in the case of the
parallel layout, an adequate installation space (packaging space),
required for installing speed reducer 60 on lower arm 20, can be
defined between the rotation axis of motor 50 and turning portion
23. Thus, even when utilizing the downsized electric motor whose
output torque is small, it is possible to certainly produce a
required steering torque by way of speed reducer 60 having an
adequately high reduction ratio. Furthermore, motor 50 and speed
reducer 60 are installed on lower arm 20 but integrated with each
other on lower arm 20. More concretely, speed reducer 60 is
accommodated in the internal space R defined between first and
second cases 201-202 (upper and lower halves) constructing lower
arm 20, and additionally motor 50 is installed and fitted onto the
upper face of second case 202. That is, lower arm 20 and the
steering actuator (motor 50 and speed reducer 60) can be handled or
utilized as a unit. Thus, it is possible to enhance the saleability
of the steering apparatus of the SBW system.
(4) In steering apparatus 1 of the first embodiment shown in FIG.
1, a parallel gear train comprised of three gears 61-63 whose
rotation axes are parallel to each other, is used as a speed
reducer. In lieu thereof, a harmonic-drive speed reducer
(strain-wave gearing) may be used to reduce rotation of motor 50 at
high ratios.
As is generally known, the harmonic-drive speed reducer is based on
a principle called "strain-wave gearing". The harmonic-drive speed
reducer is comprised of three basic elements, namely, an
ellipse-shaped wave generator, a flexible flexspline, and a rigid
circular spline, all arranged concentric with each other. Such a
harmonic-drive speed reducer has the following several
advantages.
First, the harmonic-drive speed reducer can realize a comparatively
high speed reduction ratio. Furthermore, a concentric shaft
arrangement (concentric shaft geometry) of the harmonic-drive speed
reducer that input and output shafts have the same centerline,
contributes to a compact form factor. Moreover, the harmonic-drive
speed reducer has a high rotational accuracy, because of its
ability to position moving elements precisely. For instance,
suppose that such a harmonic-drive speed reducer is integrally
connected to motor 50 such that the input shaft of the
harmonic-drive speed reducer is arranged coaxial with the rotation
axis (output shaft 51) of motor 50. The harmonic-drive speed
reducer serves as a high-performance speed reducer that accurately
reduces rotation of motor output shaft 51 with a high mechanical
efficiency. As set forth above, in steering apparatus 1 of the
first embodiment, the rotation axis of motor 50 is arranged to be
offset from the pivot of axle housing 30 (i.e., the kingpin axis or
the steering axis), and thus an additional speed reducer can be
further provided between the rotation axis of motor 50 and the
kingpin axis. Because of the use of these two speed reducers,
output rotation of motor 50 is, first, reduced by means of the
harmonic-drive speed reducer, and then the reduced rotation can be
further reduced by means of the additional speed reducer (e.g.,
speed reducer 60 as shown in FIG. 1). In such a case (in the two
speed reducers combined with each other), it is possible to provide
a very high reduction ratio (in other words, adequate steering
torque), while simplifying the configuration of the additional
speed reducer (e.g., speed reducer 60 as shown in FIG. 1) provided
between the rotation axis of motor 50 and the kingpin axis.
Although the previously-discussed modification is exemplified in
the coaxial layout of the input shaft of the harmonic-drive speed
reducer and motor output shaft 51, a so-called offset arrangement
may be utilized or accepted as a high-reduction-ratio speed
changer. In the case of the offset arrangement, the input shaft of
the harmonic-drive speed reducer is arranged to be offset laterally
from the rotation axis of motor 50, and thus it is possible to
further downsize the motor unit itself.
(5) Turning portion 23 is mechanically linked via universal joint
40 to axle housing 30.
That is, universal joint 40 is configured to pivotably join or
connect axle housing 30 to lower arm 20, while permitting torque
transmission from the steering actuator (driving-side yoke 41 of
turning portion 23) to axle housing 30 (driven-side yoke 42 of
second arm 33), for realizing a steering function. That is,
universal joint 40 (exactly, the center of universal joint 40)
serves as a lower outer pivot of the steered road wheel (e.g.,
front-left steered road wheel FL). Universal joint 40 is also
configured to join or connect axle housing 30 and lower arm 20, in
a manner so as to permit a vertical oscillating motion (jounce or
rebound) of the steered road wheel (e.g., front-left steered road
wheel FL) with respect to the vehicle body, for realizing a
suspension function. Therefore, by means of a simple linkage
structure (i.e., only one universal joint 40), it is possible to
reconcile both the smooth steering function and the smooth
suspending function.
(6) Motor 50 is installed on the upside of lower arm 20.
Therefore, as compared to a lower-arm-underside-mounted steering
actuator in which an electric motor is installed on the underside
of the lower arm, in the case of the lower-arm-upside-mounted
steering actuator (see FIG. 1) in which motor 50 is installed on
the upside of lower arm 20, it is possible to certainly prevent
motor 50 (an electronically-controlled precision mechanical
instrument) from being damaged due to obstacles on the road
surface, while certainly avoiding undesired interference between
the steering actuator and the obstacles during driving of the
vehicle. Additionally, owing to the offset layout of steering
apparatus 1 in which motor 50 and speed reducer 60 are installed on
lower arm 20 but integrated with each other on the same lower arm
20, it is possible to downsize the motor unit itself. Because of
the downsized motor unit, even when motor 50 is installed on the
upside of lower arm 20 on front-wheel-drive vehicles, it is
possible to prevent undesired interference between drive shaft DS
and motor 50.
(7) A pair of steering actuators, each of which is comprised of
motor 50 and speed reducer 60, are installed for respective steered
road wheels (e.g., front-left and front-right steered road wheels
FL-FR).
Therefore, it is possible to enhance the layout flexibility and the
design flexibility of several devices constructing the automotive
SBW vehicle steering system. It is possible to realize the totally
downsized and compactified steering system configuration.
Furthermore, left and right steered road wheels (e.g., front-left
and front-right steered road wheels FL-FR) can be steered
independently of each other by means of respective steering
actuators, thereby enhancing the maneuverability of the vehicle.
Moreover, it is possible to supply a combined unit, which is
produced by combining a suspension-system component part (i.e.,
lower arm 20) with a steering-system component part (i.e., the
steering actuator incorporated in steering apparatus 1 and
comprised of motor 50 and speed reducer 60), as a subassembly for
each steered road wheel (for each of steered front road wheels
FL-FR). This contributes to the further enhanced saleability.
Moreover, a fail-safe mechanism (or a back-up system) may be
further added, so as to execute a back-up operating mode at which a
pair of steering actuators are mechanically coupled to each other
via the back-up system (e.g., a back-up cable) in the presence of
an SBW system failure (e.g., in the presence of a steering actuator
failure). By the provision of such a back-up system, even when one
of the left and right steering actuators becomes failed, part of
steering torque generated from the other unfailed steering actuator
can be transmitted via the back-up cable to the failed steering
actuator, for properly steering each of the steered road wheels
(front steered road wheels FL-FR).
(8) Additionally, steering controller S-ECU, which is configured to
electronically control electric motor 50, is installed on lower arm
20 on which motor 50 is installed.
Therefore, it is possible to supply a combined unit, which is
produced by combining a suspension-system component part (i.e.,
lower arm 20), a steering-system component part (i.e., the steering
actuator incorporated in steering apparatus 1 and comprised of
motor 50 and speed reducer 60), and steering controller S-ECU with
each other, as a subassembly for each steered road wheel (for each
of steered front road wheels FL-FR). This contributes to the
more-improved saleability.
Second Embodiment
Referring now to FIGS. 2-3, there is shown the steering apparatus 1
of the second embodiment. In a similar manner to the first
embodiment of FIG. 1, steering apparatus 1 of the second embodiment
is also applied to a steer-by-wire (SBW) system of an automotive
vehicle, in which front-left and front-right steered road wheels
FL, FR, each rotatably supported by suspension system 2, are
steered independently of each other by driving forces produced by
respective steering actuators, each comprised of electric motor 50,
a speed reducer denoted by reference sign 70, and a link mechanism
denoted by reference sign 80.
(Steering System Configuration)
Steering apparatus 1 of the second embodiment is hereunder
described in detail in reference to FIGS. 2-3. In explaining the
second embodiment, for the purpose of simplification of the
disclosure, the same reference signs used to designate elements in
the first embodiment will be applied to the corresponding elements
used in the second embodiment, while detailed description of the
same reference signs will be omitted because the above description
thereon seems to be self-explanatory. Note that FIG. 2 shows the
partial cross-sectional view of only the front-left side of
steering apparatus 1 of the second embodiment, when viewed from the
front face of the vehicle, and the partial cross section of FIG. 2
is taken along the line C-C in FIG. 3. On the other hand, FIG. 3
shows the partial cross-section of steering apparatus 1 of the
second embodiment, when viewed from the upside of the vehicle. In
FIG. 2, a part of link mechanism 80 is omitted, whereas in FIG. 3
strut 10, drive shaft DS, axle housing 30, wheel bearing 31, and
wheel hub H, and the like are omitted. In a similar manner to the
first embodiment, suspension system 2 shown in FIGS. 2-3 is a strut
type suspension system with strut 10 employing both a coil spring
and a shock absorber.
Lower arm 20 shown in FIGS. 2-3 is a .GAMMA.-shaped lower control
arm, which is generally used as a strut-type front suspension
system. Lower arm 20 is pivotally or oscillatingly supported on the
vehicle body by means of two lower-arm pivots, corresponding to
"supporting portions" denoted by reference signs 21a, 21b in FIG.
3. The structures of supporting portions 21a-21b of FIG. 3 are
identical to those of supporting portions 21, 21 of the first
embodiment shown in FIG. 1.
As viewed from the upside of the vehicle, that is, in the
longitudinal direction of the vehicle, turning portion 23 of lower
arm 20 is located at almost the same position as axle shaft AS
(i.e., the rotation axis of front-left steered road wheel FL).
Additionally, turning portion 23 of lower arm 20 is arranged closer
to the front supporting portion 21a rather than the rear supporting
portion 21b. Second arm 33 of axle housing 30 is linked via a ball
joint 90 to turning portion 23. In the second embodiment, ball
joint 90 has the same structure as a typical road-wheel side
control-arm supporting portion generally applied to a typical
.GAMMA.-shaped lower control arm not employing a steering actuator.
Also, ball joint 90 is linked to the road wheel side (axle housing
30) at the same installation position as the typical road-wheel
side control-arm supporting portion. The axis of a ball stud 91 of
ball joint 90 is arranged to extend substantially in the vertical
direction (in the direction of the vehicle z-axis). Ball joint 90
serves to absorb an angle change between axle housing 30 and lower
arm 20, occurring due to oscillating motion of lower arm 20.
Speed reducer 70 is installed on the inside end portion of lower
arm 20 in the lateral direction (in the direction of the vehicle
y-axis). Concretely, three gears 71-73, constructing speed reducer
70, are built in arm portion 22 of lower arm 20. On the other hand,
link mechanism 80 is installed on the outside of lower arm 20 in
the lateral direction (in the direction of the vehicle y-axis).
Concretely, a plurality of arms and rods, constructing link
mechanism 80, are mounted on arm portion 22 of lower arm 20 (see
FIG. 3). Link mechanism 80 is provided to transmit rotation reduced
by speed reducer 70 and torque multiplied by speed reducer 70 via
turning portion 23 to second arm 33 of axle housing 30. As a result
of this, second arm 33 turns or pivots. That is, lower arm 20
pivotably supports axle housing 30 by means of turning portion 23.
Ball joint 90 serves as a lower outer pivot of front-left steered
road wheel FL. On the other hand, the installation point of the
upper end of strut 10 to the vehicle body serves as an upper outer
pivot of front-left steered road wheel FL. Therefore, the straight
line, linking the installation point of the upper end of strut 10
to the vehicle body (i.e., the upper outer pivot) and ball joint 90
(i.e., the lower outer pivot), corresponds to a kingpin axis (i.e.,
a steering axis) of front-left steered road wheel FL.
(Steering Actuator)
The steering actuator of steering apparatus 1 of the second
embodiment is comprised of motor 50, speed reducer 70, and link
mechanism 80. The steering actuator is installed on the upper face
of lower arm 20 or the side face of lower arm 20, or installed
inside of lower arm 20. In a similar manner to the first
embodiment, an indicated by the phantom line in FIGS. 2-3 the
steering controller S-ECU, which is configured to control motor 50,
is installed or mounted on lower arm 20 in close proximity to the
motor.
Lower arm 20 has a first case 221 constructing the lower face of
lower arm 20, a second case 222 installed on the upper face of the
first case 221, and third and fourth cases 223-224 installed on the
upper face of the second case 222. These four cases 221-224
cooperate with each other to provide a speed-reducer casing for
speed reducer 70.
Speed reducer 70 is constructed by a two-stage gear mechanism using
a worm gear system. First gear 71 is a worm gear, second gear 72 is
a worm wheel (a large-diameter gear 721), and third gear 73 is a
sector gear.
In a similar manner to the first embodiment, in steering apparatus
1 of the second embodiment, electric motor 50 is a direct-current
(DC) brushless motor. The rotation axis of motor 50 is arranged
along the axes of two rubber-bushed supporting portions 21a, 21b,
which axes are arranged substantially coaxial with each other in
their longitudinal directions (in the direction of the vehicle
x-axis). Thus, the straight line, linking the axes of two
rubber-bushed supporting portions 21a, 21b, and the rotation axis
(motor output shaft 51) of motor 50 are arranged substantially
parallel to each other. Additionally, motor 50 is laterally spaced
apart from turning portion 23 and arranged close to the axis of
oscillating motion of lower arm 20 (that is, the straight line
through the axes of supporting portions 21a-21b). More concretely,
motor 50 is installed on the upper face of first case 221 and
located between front and rear supporting portions 21a-21b and
arranged closer to the rear supporting portion 21b rather than the
front supporting portion 21a.
Output shaft 51 of motor 50 is accommodated in third case 223.
First gear 71 is fixedly connected to the tip of output shaft 51,
for co-rotation with the motor output shaft. Second gear 72 is
provided in third case 223 and arranged to be laterally outwards
offset from motor output shaft 51. Second gear 72 is rotatably
supported by means of a bearing BRG11 installed in second case 222
and a bearing BRG12 installed in first case 221. The rotation axis
(a rotational shaft 720) of second gear 72 is arranged to extend in
the vertical direction (in the direction of the vehicle z-axis)
perpendicularly to a plane of lower arm 20, and laid to be
laterally outwards offset from motor output shaft 51.
Large-diameter gear 721 (the worm wheel) and a small-diameter spur
gear 722 are formed integral with rotational shaft 720 of second
gear 72 to provide a two-stage gear configuration. Large-diameter
gear 721 (the worm wheel), located above small-diameter spur gear
722, is in meshed-engagement with first gear 71 (the worm gear)
Third gear 73 is installed on the outside of second gear 72 in the
lateral direction (in the direction of the vehicle y-axis). Third
gear 73 is rotatably supported by means of a bearing BRG13
installed in first case 221 and a bearing BRG14 installed in fourth
case 224. The rotation axis (a rotational shaft 730) of third gear
73 is arranged in parallel with the rotation axis (rotational shaft
720) of second gear 72. The toothed portion of third gear 73 (the
sector gear) is in meshed-engagement with small-diameter gear 722
of second gear 72. The rotation axis (rotational shaft 730) of
third gear 73 is arranged to protrude upwards from the upper face
of lower arm 20, while penetrating second and fourth cases 222 and
224.
A third-gear housing section 225 of first case 221, in which third
gear 73 (the sector gear) is accommodated, is formed into a sector.
A pair of radially-extending sidewall portions S1, S2 of third-gear
housing section 225 serve as respective stopper shoulders (a
stopper mechanism). An excessive anticlockwise angular displacement
(viewing FIG. 3) of third gear 73 exceeding a predetermined
anticlockwise angular-displacement limit is restricted by way of
abutment of a first one S1 of the two stopper shoulders (S1, S2)
with one radially-extending sidewall portion 731 of third gear 73
(the sector gear). In a similar manner, an excessive clockwise
angular displacement (viewing FIG. 3) of third gear 73 exceeding a
predetermined clockwise angular-displacement limit is restricted by
way of abutment of the second stopper shoulder S2 with the other
radially-extending sidewall portion 732 of third gear 73. The
upside view of FIG. 3 shows the neutral position of third gear 73
at which the steer angle of steered front-left road wheel FL is
"0". As discussed above, third-gear housing section 225, in which
third gear 73 (the sector gear) is accommodated, is provided with a
stopper mechanism (first and second stopper shoulders S1-S2) that
restricts excessive anticlockwise and clockwise angular
displacements of third gear 73 exceeding the predetermined
angular-displacement limits. The previously-discussed predetermined
angular-displacement limits are set or determined to be identical
to maximum leftward and rightward rotation angles of third gear 73
(the sector gear) under left-turn and right-turn limits.
With the previously-discussed speed reducer 70, rotation of motor
50 is reduced by means of the two-stage speed reducer 70, and then
the reduced speed is transmitted to third gear 73. At the same
time, an output torque generated from motor 50 is multiplied in
proportion to the speed reduction ratio of the two-stage speed
reducer 70, and then the multiplied torque is outputted to third
gear 73. Rotation and torque of third gear 73 are transferred via
link mechanism 80 to second arm 33 of axle housing 30, to turn axle
housing 30 (in other words, front-left steered road wheel FL) about
the kingpin axis (the steering axis). That is, axle housing 30 (in
other words, front-left steered road wheel FL) is turned by a
driving force of motor 50 installed on lower arm 20.
In the same manner as the first embodiment, in the steering
apparatus of the second embodiment, third gear 73 is constructed by
a sector gear, and thus third-gear housing section 225, in which
third gear 73 (the sector gear) is accommodated, can be shaped into
a sector form, which is configured to be substantially conformable
to the outline of the sector gear (third gear 73), fully taking
into account the operating range (or the working area) of the
sector gear. Therefore, it is possible to effectively reduce or
shorten the size and dimensions of lower arm 20 in the lateral and
longitudinal directions (in the directions of the y-axis and the
x-axis of the vehicle). Hence, it is possible to suppress lower arm
20 from being lengthened than necessary, while adequately reducing
the motor speed, thereby enabling the compactified SBW system.
Additionally, motor 50 is installed on the upper face of first case
211, such that the projected area of the front face of motor 50
becomes minimum, when viewed in the longitudinal direction (in the
direction of the vehicle x-axis). Thus, there is no risk of
undesired interference between motor 50 and vehicle-body side
component parts (such as engine component parts), thereby avoiding
the layout flexibility from lowering. Furthermore, motor 50 is
installed between front and rear supporting portions 21a-21b and
arranged closer to the rear supporting portion 21b rather than the
front supporting portion 21a. As viewed from above (in the top view
of the vehicle), motor 50 is laid out, such that motor 50 and drive
shaft DS are not overlapped with each other. Thus, even when lower
arm 20 oscillates during suspension stroke, there is no risk that
motor 50 comes into contact with drive shaft DS.
In addition to the above, as seen in FIG. 2, the positional
relationship between the speed-reducer casing (especially, third
case 223) and drive shaft DS is configured or designed, such that a
clearance space .alpha. is ensured or defined between the uppermost
face of lower arm 20 (that is, the top face of third case 223) and
the lowermost end of drive shaft DS during full rebound of the
suspension-system control arm. Hence, even when lower arm 20 is
oscillating during suspension stroke, there is no risk that the
upper end of lower arm 20 (exactly, the top face of third case 223)
comes into contact with drive shaft DS.
Moreover, as seen in FIG. 2, the positional relationship between
the speed-reducer casing (especially, first case 221) and turning
portion 23 of lower arm 20 is configured or designed, such that a
clearance space .beta. is ensured or defined between the lowermost
face of the inside end portion of lower arm 20 (that is, the
lowermost face of first case 221) and the horizontal plane passing
through the lowermost end of turning portion 23. That is to say,
the lowermost end face of lower arm 20 is configured or designed
not to protrude downwards than necessary, and thus there is no risk
of undesired interference between lower arm 20 and obstacles on the
road surface.
Link mechanism 80 has the same structure as a typical
steering-output linkage (e.g., rack-and-pinion steering gear)
generally applied to a typical steering system differing from a
steer-by-wire system. In the second embodiment, link mechanism 80
is comprised of a pitman arm 81, a tie rod 82, and a steering
knuckle arm 83. Link mechanism 80 serves to convert rotary motion
reduced by speed reducer 70 (that is, output rotation of third gear
73) into pivoting motion of axle housing 30 via turning portion
23.
One end 81a of pitman arm 81 is integrally (fixedly) connected to
the tip of third-gear rotational shaft 730, which tip protrudes
upwards from the upper face of lower arm 20. As can be seen in FIG.
3, in the neutral state where the steer angle of steered front-left
road wheel FL is "0", pitman arm 81 is arranged along the
longitudinal direction (in the direction of the vehicle x-axis),
such that the neutral axis of pitman arm 81 is arranged parallel
with the longitudinal direction. Pitman arm 81 is pivotable about
the end 81a (the center of oscillating or pivoting motion of pitman
arm 81). The other end 81b of pitman arm 81 is linked via a ball
joint to one end 82a of tie rod 82.
Tie rod 82 is arranged in the lateral direction (in the vehicle
y-axis). The other end 82b of tie rod 82 is linked via a ball joint
to one end 83a of knuckle arm 83.
In a similar manner to pitman arm 81, in the neutral state shown in
FIG. 3, where the steer angle of steered front-left road wheel FL
is "0", knuckle arm 83 is arranged along the longitudinal direction
(in the direction of the vehicle x-axis). The other end 83b of
knuckle arm 83 is integrally (fixedly) connected to second arm 33
of axle housing 30.
The longitudinal length of knuckle arm 83 is dimensioned to be
substantially identical to that of pitman arm 81. The first end 81a
of pitman arm 81 and the second end 83b of knuckle arm 83 are
arranged at almost the same position in the longitudinal direction
(the vehicle x-axis direction). Additionally, the straight line L
through (i) the rotation center of the turning pair of the second
end 82b of tie rod 82 and the first end 83a of knuckle arm 83 (that
is, the rotation center D of the ball joint linking tie rod 82 and
knuckle arm 83) and (ii) the rotation center of the turning pair of
turning portion 23 of lower arm 20 and second arm 33 of axle
housing 30 (that is, the rotation center E of ball joint 90 linking
turning portion 23 and second arm 33), is arranged substantially
parallel to the pivot of oscillating motion (pivoting motion) of
lower arm 20.
The operation of link mechanism 80 is hereunder described in
detail. Pitman arm 81 pivots or oscillates by way of rotary motion
of third gear 73. In other words, the rotary motion of third gear
73 is translated into an oscillating motion of pitman arm 81. The
oscillating motion of pitman arm 81 is translated into a
displacement of tie rod 82 in the lateral direction (in the
direction of the vehicle y-axis). The lateral displacement of tie
rod 82 is translated into an oscillating motion of knuckle arm 83.
The oscillating motion of knuckle arm 83 is translated into a
pivoting motion (or a turning motion) of second arm 33 of axle
housing 30, which is integrally (fixedly) connected to knuckle arm
83. Ball joint 90 serves as the center of the turning motion of
second arm 33 with respect to lower arm 20. On the assumption that
front-left steered road wheel FL is an inside steered road wheel, a
maximum angle of the turning motion of second arm 33, measured from
the previously-noted neutral state (zero average steer angle), that
is, a maximum steer angle (an angular-displacement limit value) at
the inside steered road wheel is set to become approximately 40
degrees (see FIG. 3).
In a similar manner to the front-left steering system configuration
as discussed previously, the steering actuator (motor 50, speed
reducer 70, and link mechanism 80) of steering apparatus 1 of the
second embodiment is installed on lower arm 20 of the front-right
side. That is, the steering actuator (50, 70, 80) is installed on
each individual steered road wheel (FL, FR). These left and right
steering actuators construct a part of the SBW system.
Operation and Effects of Second Embodiment
Steering apparatus 1 of the second embodiment provides the
following operation and effects.
In addition to the steering system configurations (1), (2), (3),
(6), and (7) and their operation and effects of the steering
apparatus of the first embodiment, the steering apparatus of the
second embodiment can further provide the following operation and
effects by system configurations (9), (10), (11), (12), and
(13).
(9) Lower arm 20 is pivotally supported on the vehicle body by
means of two supporting portions 21a, 21b spaced apart from each
other, and additionally motor 50 is installed between these
supporting portions 21a, 21b.
As set forth above, motor 50, which serves as a major heavy load of
the steering actuator, is arranged in close proximity to the pivot
of oscillating motion (pivoting motion) of lower arm 20 (that is,
the straight line through two supporting portions 21a, 21b). Thus,
the distance between the installation position of motor 50 and the
pivot (the center of oscillating motion) of lower arm 20 can be
remarkably shortened. As a result of this, it is possible to
greatly reduce a moment of the motor load acting on lower arm 20
down to approximately a zero moment, thus certainly suppressing an
increase in unsprung mass of the vehicle.
(10) The rotation axis of motor 50 (i.e., motor output shaft 51) is
arranged along the axes of supporting portions 21a-21b, pivotably
or oscillatingly supporting lower arm 20, which axes are arranged
substantially coaxial with each other in the direction of the
vehicle x-axis and serve as pivots for lower arm 20. Speed reducer
70 is constructed by a worm gear system (a worm gearing speed
reducer) having a worm gear (first gear 71) and a worm wheel
(second gear 72).
Such a worm gearing speed reducer can provide a very high speed
reduction ratio. Additionally, the rotation axis of motor 50 (motor
output shaft 51) is arranged along the lower-arm pivots (supporting
portions 21a-21b) arranged substantially coaxial with each other in
the direction of the vehicle x-axis, and therefore the projected
area of the front face of motor 50 becomes minimum. Thus, there is
no risk of undesired interference between motor 50 and vehicle-body
side component parts (such as engine component parts), thereby
avoiding the layout flexibility from lowering. Furthermore, both
faces of the worm wheel (second gear 72) are arranged parallel to
the horizontal plane, thereby suppressing the vertical dimension of
lower arm 20 from undesirably lengthening. Because of the
previously-noted horizontal layout of the worm wheel (that is, the
suppressed or reduced vertical dimension of lower arm 20), it is
possible to ensure a clearance space .alpha. between the uppermost
face of the top face of third case 223 of lower arm 20 and the
lowermost end of drive shaft DS during full rebound of the
suspension-system control arm, thereby preventing the upper end of
lower arm 20 (the top face of third case 223) from coming into
contact with drive shaft DS during suspension stroke. Moreover,
because of the suppressed or reduced vertical dimension of lower
arm 20, it is possible to ensure a clearance space .beta. between
the lowermost face of first case 221 of lower arm 20 and the
horizontal plane passing through the lowermost end of turning
portion 23, thereby preventing the lower end of lower arm 20 from
coming into contact with obstacles on the road surface, during
driving of the vehicle. Therefore, in addition to the
aforementioned effects obtained by the system configuration (9), it
is possible to ensure a very high speed reduction ratio without
sacrificing the essential suspension function of the suspension
system.
(11) Speed reducer 70 is accommodated in the speed-reducer casing
(first to fourth cases 221-224) and has a sector gear (third gear
73). The speed-reducer casing (especially, third-gear housing
section 225 of first case 221) is provided with a stopper mechanism
S1-S2 that restricts excessive anticlockwise and clockwise angular
displacements of the sector gear (third gear 73) exceeding
predetermined angular-displacement limits.
By utilizing a sector gear as the third gear 73, constructing a
part of speed reducer 70, third-gear housing section 225 of first
case 221 of lower arm 20 can be shaped into a sector form, which is
configured to be substantially conformable to the outline of the
sector gear (third gear 73), fully taking into account the
operating range (or the working area) of the sector gear.
Therefore, it is possible to effectively reduce or shorten the size
and dimensions of lower arm 20 in the lateral and longitudinal
directions (in the directions of the y-axis and the x-axis of the
vehicle). Hence, it is possible to reconcile both the adequately
reduced motor speed and the properly downsized lower arm 20,
thereby enabling the compactified SBW system. Furthermore,
third-gear housing section 225 of first case 221 is provided with a
stopper mechanism S1-S2 that restricts excessive anticlockwise and
clockwise angular displacements of the sector gear (third gear 73)
exceeding predetermined angular-displacement limits. The
aforementioned predetermined angular-displacement limits are set or
determined to be identical to maximum leftward and rightward
rotation angles of third gear 73 (the sector gear) under left-turn
and right-turn limits. That is, speed reducer 70 has a
speed-reducing function, and also has a stopper function that
mechanically sets leftward and rightward steer angle limits. This
eliminates the necessity of an additional stopper device, thus
ensuring reduced number of system component parts and enhanced
fail-safe function and lower system installation time and
costs.
In the speed reducer 70 employed in steering apparatus 1 of the
second embodiment described previously in reference to FIGS. 2-3,
speed reducer 70 is constructed by three gears, namely, the worm
gear (first gear 71), the worm wheel (second gear 72), and the
sector gear (third gear 73). In lieu thereof, third gear 73 may be
used as a worm sector. In such a case, second gear 72 (the worm
wheel) is omitted and third gear 73 (the worm sector) is kept
directly in meshed-engagement with first gear 71. The modification
contributes to more-reduced number of system component parts and
enhanced fail-safe function and lower system installation time and
costs.
(12) Also provided as link mechanism 80 employed in steering
apparatus 1 of the second embodiment are tie rod 82 displaceable in
the lateral direction (in the direction of the vehicle y-axis)
responsively to rotary motion of motor 50, and knuckle arm 83
integrally (fixedly) connected to axle housing 30 and mechanically
linked to tie rod 82. Additionally, the straight line L passing
through (i) the rotation center of the turning pair of tie rod 82
and knuckle arm 83 (that is, the rotation center D of the ball
joint linking tie rod 82 and knuckle arm 83) and (ii) the rotation
center of the turning pair of lower arm 20 and axle housing 30
(that is, the rotation center E of ball joint 90 linking lower arm
20 and axle housing 30), is arranged substantially parallel to the
pivot of oscillating motion (pivoting motion) of lower arm 20.
By the provision of link mechanism 80 having tie rod 82 and knuckle
arm 83, it is unnecessary to mount speed reducer 70 on the outside
end of lower arm 20. In other words, it is possible to remarkably
shorten the distance between the pivot of oscillating motion of
lower arm 20 and the installation position of speed reducer 70
(especially, motor 50). As a result of this, it is possible to
greatly reduce a moment of the load acting on speed reducer 70 down
to a minimum, thus certainly suppressing an increase in unsprung
mass of the vehicle.
Furthermore, in the neutral position where the steer angle of a
steered road wheel (e.g., steered front-left road wheel FL) is "0",
the angle between tie rod 82 and knuckle arm 83 becomes
approximately a right angle (90 degrees). Even when tie rod 82
displaces from its neutral state leftwards or rightwards, a moment
of force inputted from tie rod 82 to knuckle arm 83 becomes
maximum. There is no deviation between (i) the change in angular
displacement (clockwise displacement in FIG. 3) of knuckle arm 83
per unit inward displacement of tie rod 82 and (ii) the change in
angular displacement (anticlockwise displacement in FIG. 3) of
knuckle arm 83 per unit outward displacement of tie rod 82. For the
reasons discussed above, such a linkage layout enables stable steer
angle control as well as efficient torque transmit from speed
reducer 70 to axle housing 30. This contributes to the downsized
speed reducer (the downsized motor). This also contributes to the
more-simplified steering control logic.
Moreover, the inside end of tie rod 82 is installed on lower arm 20
(exactly, linked to pitman arm 81 installed on lower arm 20). By
virtue of the installation of tie rod 82 on lower arm 82, there is
a less change in the positional relationship between tie rod 82 and
the suspension-system control arm (i.e., lower arm 20), and as a
result any toe change does not occur during suspension stroke.
Thus, the previously-discussed system configuration (12) of
steering apparatus 1 of the second embodiment, in which the
steering actuator (motor 50 and speed reducer 70) is linked via
link mechanism 80 to axle housing 30, can provide the same effects
as the system configurations (1), (2), (3), (6) and (7) of steering
apparatus 1 of the first embodiment.
(13) In steering apparatus 1 of the second embodiment shown in
FIGS. 2-3, a two-stage worm-gearing speed reducer comprised of
first gear 71 (the worm gear), second gear 72 (the worm wheel), and
third gear 73 (the sector gear), is used as a speed reducer. In
lieu thereof, a harmonic-drive speed reducer (strain-wave gearing)
may be used to reduce rotation of motor 50 at high ratios.
In such a case, the worm gearing, composed of first gear 71 (the
worm gear) and second gear 72 (the worm wheel), is omitted. In lieu
thereof, a harmonic-drive speed reducer is integrally connected to
motor 50 such that the input shaft of the harmonic-drive speed
reducer is arranged coaxial with the rotation axis (output shaft
51) of motor 50. Additionally, the sub-assembly of motor 50 and the
harmonic-drive speed reducer is installed on the upper face of
lower arm 20, such that rotational shaft 720 of second gear 72 is
replaced with the output shaft of the harmonic-drive speed reducer,
and that a gear, fixedly connected to the output shaft of the
harmonic-drive speed reducer, is kept in meshed-engagement with
third gear 73 (the sector gear). Such a harmonic-drive speed
reducer contributes to a compact form factor and more-simplified
speed reducer configuration. When installing the sub-assembly of
motor 50 and the harmonic-drive speed reducer on lower arm 20, the
installation position of motor 50 must be properly adjusted in the
vehicle longitudinal direction, so as to avoid undesirable
interference between drive shaft DS and motor 50. In the case of
application of the harmonic-drive speed reducer equipped steering
actuator to a front steered road wheel of a rear-wheel-drive
vehicle, it is possible to easily optimize or determine the
installation position of motor 50 without any interference between
drive shaft DS and motor 50.
[Modifications ]
In the shown embodiments, steering apparatus 1 is applied to a
MacPherson strut-type suspension system. Steering apparatus 1 may
be applied to the other type of suspension systems, for example, a
double-wishbone type suspension system using two lateral control
arms (upper and lower control arms), or a short-long arm (SLA)
suspension system using an upper short-length control arm/link
(e.g., an A-shaped arm or a lateral link) and a lower long-length
control arm (e.g., an A-shaped arm). That is, the steering
apparatus 1 of the shown embodiment can be applied to any types of
suspension systems employing at least a lower suspension-system
control arm.
In the first embodiment (see FIG. 1), a Hooke's joint is used as
universal joint 40, which mechanically links turning portion 23 of
lower arm 20 to axle housing 30. Instead of using such a Hooke's
joint (a very simple universal joint), another type of universal
joint may be used. For instance, turning portion 23 of lower arm 20
may be linked to axle housing 30 via a constant-velocity universal
joint that transmits power at constant angular velocity from the
driving to the driven shaft.
In the second embodiment (see FIGS. 2-3), tie rod 82 (link
mechanism 80) is arranged just forward of lower arm 20. In lieu
thereof, tie rod 82 (link mechanism 80) may be arranged just
backward of lower arm 20. On the other hand, the positional
relationship between tie rod 82 and lower arm 20 in the vehicle
vertical direction can be suitably set or configured.
The entire contents of Japanese Patent Application No. 2007-220691
(filed Aug. 28, 2007) are incorporated herein by reference.
While the foregoing is a description of the preferred embodiments
carried out the invention, it will be understood that the invention
is not limited to the particular embodiments shown and described
herein, but that various changes and modifications may be made
without departing from the scope or spirit of this invention as
defined by the following claims.
* * * * *